Such assemblies, usable in numerous fields for the distribution and circulation of gas, and particularly for anesthetic apparatus for their ease of cleaning and disinfection by simply disassembling the cover and the body, can have complicated structure according to the number of the portions of conduits, thereby multiplying the number of sealing strips. Until the present, these sealing strips have been constituted by joints, generally of trapezoidal section, cut off in length and disposed manually in recesses of the cover, which requires skilled hand labor and considerable mounting time, at the same time not permitting eliminating risk of poor sealing, particularly in the region in which the joints are closed.